An improved apparatus for encapsulating a finely divided clay within an organic polymeric material

ABSTRACT

An improved apparatus for encapsulating a finely divided clay within an organic polymeric material comprises a pin mixer having a container inclined to the horizontal, and a rotatable shaft therein carrying pins defining a helix of decreasing pitch from the upper inlet end to the lower discharge end of the mixer.

[451 Apr. 30, 1974 United States Patent [191 Grillo et a1.

1.7x ww /5 MWN 3 m mmmA mmmw ww amA as; w "O f Pe .finm FACE men mw w0062 M O F 1,147,185 4/1969 Great 259/7 224,397 4/1962 415/72 [75]Inventors: Thomas A. Grillo; Walter Eugene Morris, both of Macon, Ga.

Assignee: J. M. Huber Corporation, Locust Primary Examinerl-larvey C.Homsby Assistant ExaminerAlan I. Cantor Attorney, Agent, or Firm-HaroldH. Flanders; Donald S. Lilly [22] Filed: June 21, 1971 Appl. No.:155,173

[57] ABSTRACT An improved apparatus for encapsulating a finely dividedclay within an organic polymeric material com- [52] US. 259/ 7, 259/DIG.13 [51] B01f 7/04, BOlf 7/08 Int. Cl.

[58] Field of Search............. 259/7, 22, 42, 65, 106, 259/191, 194,DIG. 13, D16. 24; 416/176, 200

prises a pin mixer having a container inclined to the horizontal and arotatable shaft therein carrying pins 5 References Cited defining ahelix of decreasing pitch from the upper UNITED STATES PATENTS inlet endto the lower discharge end of the mixer.

259/7 1 Claim, 1 Drawing Figure AN IMPROVED APPARATUS FOR ENCAPSULATINGA FINELY DIVIDED CLAY WITHIN AN ORGANIC POLYMERIC MATERIAL BACKGROUND OFTHE INVENTION This invention relates generally to an improved apparatusfor encapsulating a finely divided clay within an organic polymericmaterial in the production of record materials, of the type having asensitized surface which reacts to a colorless ink applied thereto bydisplaying distinctive colors in the image-configurated areas where saidink is present.

Within recent years a highly successful recording system has come intouse based upon a multiple coloring principle in which an oily ink havingtwo types of chromogenic reactants, normally colorless, is used upon anink-receiving sheet sensitized with materials which react respectivelywith the two chromogenic substances to yield distinctive coloration. Inone version of such system the said ink-receiving sheet is sensitizedwith substantially insoluble acid-like materials of high surfaceactivity, such as attapulgite and zeolite, the chromogenic reactantsbeing such substances as Crystal Violet Lactone and Benzoyl LeucoMethylene Blue. Such a system is disclosed, for example, in U. S. Pat.No. 2,712,507 to Barrett K. Green, pertaining to the well-known NCRpaper (the quoted phrase being a trademark ofthe National Cash RegisterCompany), wherein the said ink is applied from an oversheet by pressurerelease from microscopic capsules. In recording systems of this type thecoloration of Crystal Violet Lactone is effected by an electrondonor-acceptor solid-surface reaction with the acid clay like mineraland the coloration of the Benzoyl Leuco Methylene Blue is brought aboutby hydrolysis followed by an oxidation reduction reaction.

Because of the considerable time differential present with respect tocompletion of the two coloration reactions for the Crystal VioletLactone and the Benzoyl Leuco Methylene Blue, an hiatus is often foundto exist in the continuity of existence of the recorded marks producedby the previously described system. As such problem has beendemonstrated to largely result from the fact that the two colorationreactions occur entirely via solid-surface reaction, improved recordmembers have been developed wherein the coloration reactions are notdependent upon absorption on a solid surfaceactive material. Such animproved system is set forth, for example, in U. S. Pat. No. 3,455,721,wherein a record member is disclosed carrying in recording areas twotypes of microfine particles: the first an oil soluble acid-reactantorganic polymeric material; the second, a colorless acid-type of mineralsuch as kaolin clay. When the previously described oily ink is appliedto such a member, the polymeric particles enter the oil solution andpromptly bring about the electron donoracceptor reaction which effectscoloration in Crystal Violet Lactone. At the same time contact of theoily ink with the acid type mineral initiates the oxidation reductionreaction which in time colorates the Benzoyl Leuco Methylene Blue dye.Because coloration of the Crystal Violet Lactone occurs in solution, thecolored material is capable of entering the support sheet, and thiscoupled with the absence of particle contamination such as occurs wheresurface active particles are used,

assures much greater persistence in coloration of the said dye.

Additional disclosures relative to the state of the art in which thepresent invention occurred may be found in U. S. Pat. Nos. 2,173,346;2,463,501; 2,674,587; 3,516,845; 3,525,630; 3,535,412; British Pat. Nos.1,212,731; 1,215,618; and Canadian Pat. Nos. 852,785 and 864,009.

The concept of using both an oil soluble polymer material and anacid-type mineral in the manner as set forth above, is less thansatisfactory in the important respect that utilization of discreteparticles of the one and of the other materials necessarily introducesundesirable discontinuitives into the recording surface, with aconsequent loss of resolution and uniformity in the marking qualities ofsuch surface. In particular it will be evident that even with the mostuniform distribution of discrete particles, one particle type beinguniformly dispensed among the other, coloration will occur whether inthe case of Crystal Violet Lactone or of Benzoyl Leuco Methylene Blue atpoints spaced by the intervening alternate type particles. Such a resultis compounded by the fact that idea] uniform distribution of one groupof particle types among the other is, of course, not achieved inpractice.

SUMMARY OF THE INVENTION In accordance with the foregoing, it may beregarded as an object of the present invention to provide an improvedapparatus for encapsulating a finely divided clay within an organicpolymeric material for use in a record member for receiving an oilycolorless ink containing chromogenic materials that react to coloraterespectively with an oil soluble acid-reactant organic polymer materialand with a colorless acid-type of mineral, wherein said polymeric andmineral materials are present at the surface of said record member'in aform yielding exceptional resolution and uniformity of recording.

It is further an object of the invention to provide an improvedapparatus for encapsulating a finely-divided clay within an organicpolymeric material to produce a clay-polymeric material compositionwhich enables the result set forth in the proceeding paragraph.

Now in accordance with the present invention, the foregoing objects, andothers as will become apparent in the cause of the ensuingspecification, are achieved by coating the base sheet of paper or otherfibroin material with a composition wherein the acid-type mineral, suchas kaolin clay, is present as a microfine dispersion of particles,individual of said particles being encapsulated within the saidpolymeric material, thereby producing a recording member the sensitizedsurface of which presents to the oily ink applied thereto an essentiallyunbroken polymeric layer in which individual mineral particles areeffectively embedded.

The said coating composition is produced by a process wherein the heatedmineral, preferably kaolin clay, is combined with a heated liquidpolymer, preferably dispersed in a solvent, and the combined mixsubjected to high shear mixing and compaction.

A coating composition having the desired properties is produced in theherein-described process by employing an improved apparatus forencapsulating a finely divided clay within an organic polymericmaterial. This apparatus includes:

an inclined cylindrical chamber having an upper end and lower end and apair of end plates secured thereto;

a stand securing the cylindrical chamber whereby the upper end thereofis elevated with respect to the lower end; an inlet adjacent the upperend plate for introducing a mixture of clay and an organic polymericmaterial and a solvent therefore into the upper end of the chamber;

a journaled mixer shaft passing through the end plates concentricallywith the walls defining the cylindrical chamber, the shaft having anarray of rounded pins protruding therefrom and defining a helixextending about the shaft from one end to the other;

means to rotate the shaft to intimately blend the admixture of the clayand organic polymeric material and to advance the same through thechamber;

means for compacting the admixture during its passage through thechamber and prior to the discharge thereof, including the arrangement ofthe rounded pins defining the helix such that the helix decreases inpitch from the elevated or upper end of the shaft toward the opposite orlower shaft end;

and a discharge means adjacent the lower end plate for removing theencapsulated clay from the lower end of the chamber.

Thereafter the admixtures may be desolventized, preferably in thepresence of continuing shearing forces, and milled. The resultingcomposition may then be coated upon base sheet by standard methods toyield the desired recording member.

BRIEF DESCRIPTION OF THE DRAWING In the drawing appended hereto theFIGURE is a partially broken-away view of the pin mixer apparatus of thepresent invention utilized in connection with the process set forthherein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with onepreferred process for preparing the composition described herein, theacid-type mineral intended for use in the composition is initially fedto a conventional heater station.

The preferred material for such acid-type mineral is a white kaolin claysuch as, for example, the clay of this type available from the J. M.Huber Corporation of Huber, Georgia under the designation specialHydratex."

Such clays as are preferred as starting materials are generally papercoating grade clays derived from water fractionated Georgia kaolinshaving a TAPPI Brightness (in percentage reflectance) of at least 85 andapproximately 80 percent of their particle size distribution finer than2 microns with less than 6 percent of their particles coarser thanmicrons. Such clays generally have a Brookfield viscosity measured in a70 percent clay slip with a No. 1 spindle at 20 revolutions per minuteat 25 C. of 100 200 cps. Typical properties of such clays are an averageequivalent spherical particle diameter of 0.8 microns, a specificgravity of 2.60, an oil absorption of approximately 30 gms/100 gms., apH of on the order of 4.5 5.0 measured with 100 gms of clay/250 ml.water, a refractive index on the order of 1.5 1.6 and a BET surface areaon the order of 10 11 m /g.

Clays of this type are ideal for use in the present application in thatin addition to possessing the necessary acid properties, theirplate-like particle form, whiteness, and their ready availability lendthem unparalleled paper coating advantages. Other types of particulate,colorless, water and oil-insoluble acid-type clays and other mineralssuch as some of the bentonites, can also be used in the invention,although these latter materials do not possess as favorable rheologicalcharacteristics as do the kaolin clays.

When the kaolin clays are thus utilized, they will representatively beheated below 140 C., preferably to the temperature range of to C.Thereafter, the heated clay is passed to a mixing chamber where it iscombined in the presence of high intensity shearing with a suitablepolymerized resin and a diluting solvent for the resin.

The solvent may be added with the resin or may be added to the mixingchamber following addition of the resin or may in some cases asdiscussed hereinafter be omitted.

The polymerized resin materials utilized with the present invention maybe any of the substances of this type set forth in U. S. Pat. No.3,455,721, previously alluded to. Thus among the oil-soluble organicpolymeric materials suitable for use in this invention together withappropriate ink solvents to be used therewith, certain phenol-aldehydeand phenol-acetylene polymers, maleic acid-rosin resins, partially orwholly hydrolyzed styrene-maleic anhydride copolymers, ethylene-maleicanhydride copolymers, carboxy polymethylene, and wholly or partiallyhydrolyzed vinyl methyl ether-maleic anhydride copolymers are specifiedas typical of the reactive acidic polymeric materials.

Of the phenol-aldehyde resin group, examples of typically suitableresins include:

Bakelite phenolic coating materials manufactured by Union Carbide,meeting Federal Specification No. 'I"T--R27l and Military SpecificationNo. MIL--- R-15184A, which are non-heat-reactive, 100 percentparaphenylphenol, oil soluble resins having a softening point range of225 F. and a specific gravity at 25 C. of 1.20 1.23.

A p-phenylphenol resin prepared from a monomer having a generalstructural formula,

a molecular weight of 170.2, a freezing point of l66.5 C., a boilingpoint at 760 mm. Hg of 321 C., and a specific gravity at 25 C. of 1.275.

A p-sec-butylphenol resin prepared from a monomer having a generalstructural formula,

CHzra H- C ali s CHa- CH:

a molecular weight of 150.2, a boiling range at 760 mm. Hg of 237 239.7C. and a specific gravity at 25 C. of 1.037.

Bisphenol A resins prepared from a monomer having a general structuralformula,

a molecular weight of 228.3, a boiling point at 4 mm.

Hg of 220 C. and a specific gravity at 25 C. of 1.195; and other knownresins of the type described herein.

Of preferable use in the invention are the paraphenylphenol-aldehydepolymerization products. At least a dimer structure having CH OH endbonds for a terminable structure is desirable.

It is believed that a'desirable molecular weight distribution mayinclude 5 percent monomer, 15-20 trimer percent dimer, approximately 20percent timer and the remaining portions of high molecular weights.

The admixture of polymerized resin and diluting solvent which may forexample comprise xylene or the like may itself be heated on the order ofto 125 C. prior to addition to mixing chamber. Temperatures 45 in mixingchamber are maintained in the range of to 130 C. and the mix ofpolymeric material, solvent, ahd kaolin clay is therein subjected to ahigh intensity, high shear mixing and compaction action, following whichthe mix is transferred to a desolventizing chamber. The latter maysimply comprise a heat room wherein temperatures are maintained of theorder of F. to fully evaporate the solvent. During such desolventizationthe mix is preferably subjected to a shearing action as by mixer bladesor the like. Subsequently the mix is transferred to a milling stationwhich may preferably include bead grinding of the material, after whichthe product emerges in a form suitable for coating upon paper webs orother fibrous base sheets by standard techniques known in the papercoating art.

The desired high intensity, high shear mixing action described inconnection with the mixing chamber is preferably brought about by theapparatus shown in the partially sectioned, partially broken-away viewof the thereof. A power shaft 22 is joumaled by bearing blocks 24 and 26and passes into container 12' where it widens to form a mixer shaft 28.Container 12 together with the other components of the apparatus setforth are mounted upon a support stand 30, which is seen to so supportcontainer 12 that a natural gravity flow is provided through theapparatus from inlet 18 to outlet 20. Because of the flow directionspecified and the compaction action which will be set forth below it isnecessary to seal the shaft 28 22 at its lower end, and it will be seenthat a packing gland 32 is provided for such purposes.

Mixer shaft 28 is seen to be provided with a helically formed array ofrounded pins 34. Such pins 34 serve as the primary means achievingmixing and breaking up of agglomerates in apparatus 10. Typically,apparatus 10 will be operated at rotational speeds of the order of 100to 1,000 RPM, and will act both as amixer and as a mill to break up theagglomerates. It will be observed that the pitch of the helix formed bypins 34 which is suggested by the dotted line 36 in the FIGURE decreasesfrom the upper end of mixer shaft 28 toward the lower end thereof. Inconsequence of this decreasing pitch arrangement and of thegravitationally directed flow toward the shaft end with decreasingpitch, compaction and increased inner-particulate shear ensue as the mixpasses through apparatus 10. Both of these phenomena are believed to besignificant in accomplishing clay encapsulation. In particular whenmixes are thus processed in accordance with the scheme set forth it isfound that they do indeed result in coating compositions wherein thekaolin clay is thoroughly encapsulated in the polymeric materials aspreviously described, and when such mixes are thereafter utilized inpreparing coated recording members for use in record systems of the NCR"type previously referred to, that a new and superior member is enabledhaving resolution and marking qualities of a greatly improved nature. Inessence such result stems from the fact that when the compositionproduced byuse of the present invention is coated upon its support base,an essentially continuous surface of polymeric material is presented tothe reactive oily ink subsequently applied hereto, with the individualkaolin clay particles being entirely encapsulated and embedded in thepolymeric material, and thus below the immediately accessible recordsurface. I

Evidence of the fact that the above described process and apparatusactually results in the clay being encapsulated in the resin is found inthe discovery that when produced in accord with the present inventionthe resin is not separable from the clay by mechanical means, frothflotation or the like as were the resin-clays of the prior art.

A resin coating of less than 10 percent, preferably on the order of7.5%, has been found operative while prior art systems generallyrequired in excess of 15 percent resin in operative coatings. N

This reduction in resin content is significant in the economics of thesystem and provides clear evidence of the synergism produced by thepresent invention as compared with prior art physical blends.

FIGURE. A pin mixer is shown therein generally com- 65 prising acylindrical container 12 provided with upper and lower end plates 14 and16, a feed inlet 18 at the upper end thereof, and a feed outlet 20 atthe lower end The apparatus of the present invention may be employed toparticular advantage as follows:

A polymerization reaction producing, for example, a para-phenylphenol/formaldehyde resin is carried out in the absence of clay.

The resin polymerization product is made down with a solvent such asxylene. The solvent helps to extend the resin and allows for moreuniform coverage of the clay in subsequent steps. A preheated kaolinclay is added along with the resin solvent makedown to a steam heatedpin auger where the hot clay particles are coated with resin in a liquidform. The heated clay helps keep the resin fluid throughout the treatingoperation and in later steps aids in desolventizing the modified clay.The process may be carried out utilizing unheated clay if the solventlevel is increased accordingly. Sufficiently heated clay may be employedas to reduce or eliminate the need for additional heating in the mixingsteps.

Typically, the auger may be fed at the rate of 3 tons of clay per hourwith the resin-solvent flow regulated to coat the clay withapproximately 7.5 percent resin based on the clay.

The modified clay discharged from the auger may be somewhat agglomeratedand is thus passed into and through a pin mixer to reduce the averageagglomerate size and to make the modification more uniform.

The output of the pin mixer is then passed to desolventizer which is ajacketed, steam heated, double screw auger conveyor designed to removevolatiles. The solvent is vented to solvent recovery apparatus.

The desolventized, modified clay may then preferably be cooled toprevent degradation of the resin encapsulation.

Subsequently the modified clay is passed to impact mill to reduce theparticle and agglomerate size of the modified clay.

The milled product is then made down in water in slurry makedown tanks.

Following slurry makedown the slurry is passed to a bead grinding millwhich breaks down any resincemen-ted clay particles and brings theparticle size of the modified clay back in line with the starting clay.

Excessive bead grinding has a deleterious effect on the coatingproperties of the modified clay, since excess grinding removes theencapsulating resin from the clay and produces a mere physical mixtureof the resin and clay similar to the prior art compositions.

Following bead grinding at the modified clay is passed to a flocculationtank and then through filters to raise the solids content. The filtercake may then be prepared for shipment or passed to storage tanks.

in summary, a coating composition having the desired properties isproduced in the herein-described process by employing an improvedapparatus for encapsulating a finely divided clay within an organicpolymeric material. This apparatus includes:

an inclined cylindrical chamber having an upper end and lower end and apair of end plates secured thereto;

a stand securing the cylindrical chamber whereby the upper end thereofis elevated with respect to the lower end;

an inlet adjacent the upper end plate for introducing a mixture of clayand an organic polymeric material and a solvent therefore into the upperend of the chamber;

a journaled mixer shaft passing through the end plates concentricallywith the walls defining the cylindrical chamber, the shaft having anarray of rounded pins protruding therefrom and defining a helixextending about the shaft from one end to the other;

means to rotate the shaft to intimately blend the admixture of the clayand organic polymeric material and to advance the same through thechamber;

means for compacting the admixture during its passage through thechamber and prior to the discharge thereof, including the arrangement ofthe rounded pins defining the helix such that the helix decreases inpitch from the elevated or upper end of the shaft toward the opposite orlower shaft end;

and a discharge means adjacent the lower end plate for removing theencapsulated clay from the lower end of the chamber.

While the present invention has been particularly described in terms ofspecific embodiments thereof, it will be understood in view of thepresent disclosure, that numerous variations are now enabled to thoseskilled in the art, which variations in propriety, are yet within thetrue scope of the instant teaching. Accordingly the present inventionshould be broadly construed and limited only by the scope and spirit ofthe claim now appended hereto. 1

What is claimed is:

1. An improved apparatus for encapsulating a finely divided clay withinan organic polymeric material, said apparatus comprising: an inclinedcylindrical chamber having an upper end and lower end and a pair of endplates secured thereto; stand means securing said cylindrical chamberwhereby the upper end thereof is elevated with respect to the lower end,means comprising an inlet adjacent said upper end plate for introducinga mixture of clay and an organic polymeric material and a solventtherefor into the upper end of said chamher; a journaled mixer shaftpassing through said end plates concentrically with the walls definingsaid cylindrical chamber, said shaft having an array of rounded pinsprotruding therefrom and defining a helix extending about said shaftfrom one end to the other; means to rotate said shaft to intimatelyblend said admixture of the clay and organic polymeric material and toadvance same through said chamber; means for compacting said admixtureduring its passage through said chamber and prior to the dischargethereof, said means including the arrangement of the rounded pinsdefining said helix such that the helix decreases in pitch from theelevated or upper end of said shaft toward the opposite or lower shaftend, and discharge means for removing the encapsulated clay from thelower end of said chamber, said discharge means being adjacent saidlower end plate.

1. An improved apparatus for encapsulating a finely divided clay withinan organic polymeric material, said apparatus comprising: an inclinedcylindrical chamber having an upper end and lower end and a pair of endplates secured thereto; stand means securing said cylindrical chamberwhereby the upper end thereof is elevated with respect to the lower end,means comprising an inlet adjacent said upper end plate for introducinga mixture of clay and an organic polymeric material and a solventtherefor into the upper end of said chamber; a journaled mixer shaftpassing through said end plates concentrically with the walls definingsaid cylindrical chamber, said shaft having an array of rounded pinsprotruding therefrom and defining a helix extending about said shaftfrom one end to the other; means to rotate said shaft to intimatelyblend said admixture of the clay and organic polymeric material and toadvance same through said chamber; means for compacting said admixtureduring its passage through said chamber and prior to the dischargethereof, said means including the arrangement of the rounded pinsdefining said helix such that the helix decreases in pitch from theelevated or upper end of said shaft toward the opposite or lower shaftend, and discharge means for removing the encapsulated clay from thelower end of said chamber, said discharge means being adjacent saidlower end plate.